vary with loadings as well as with function. Loadings may be classified in 

 three service categories: 



(1) Severe dynamic loadings, 



(2) dynamic and static loadings, and 



(3) most stringent placement and drainage. 



Severe dynamic loading is characterized by continued abrasive movement 

 of materials adjacent to the fabric due to wave action. Dynamic and static 

 loadings are characterized by more restrictive placement procedures to 

 limit abrasive movement and include gabion applications. The most stringent 

 placement controls and drainage applications nearly eliminate abrasive 

 movement of materials adjacent to the fabric. This category includes 

 weepholes, linings of vertical walls, relief wells, linings for French and 

 trench drains, and wrap collector pipe. 



For each loading category certain construction parameters and limitations 

 must be met. In Tables 37 and 38 construction limitations for each category 

 are listed with reference to three specific applications: quarrystone revetment, 

 block revetment, and subaqueous applications. Block revetment includes pre- 

 cast cellular block (a cast or machine -produced concrete precast block having 

 continuous voids through the vertical plane normally with smooth or near 

 vertical sides) and interlocking concrete block (a cast or machine produced 

 concrete block having interengaging or overlapping edges) . The subaqueous 

 applications include groins, jetties, and breakwaters; scour protection for 

 piers, piles, and caissons; and toe aprons for bulkheads. 



Minimum geotextile filter physical, property requirements are shown in 

 Table 39 based on the construction limitations in Tables 37 and 38. Test 

 methods are described in Appendix C. The physical property requirements in 

 Table 39 are not the same as stated in the current Civil Works Construction, 

 Guide Specification, Plastic Filter Fabric, No. CW-02215 (U.S. Army, Corps of 

 Engineers, 1977). Because this report is concerned only with coastal struc- 

 tures, the test methods and requirements set forth herein are based on field 

 performance and verification in these types of structures and relevant 

 laboratory research. 



c. Filtering Integrity . 



(!) Piping Resistance Criteria . To prevent piping, it is necessary 

 to know the soil retention capability of the geotextile filter or granular 

 filter when considering a filter system. In his extensive and thorough 

 research and development project with geotextiles for filters, Calhoun 

 (1972) developed a special procedure for determining the piping resistance 

 (soil retention capacity) of fabrics. The result of this procedure, 

 described in Appendix C, was to determine the equivalent opening size (EOS) 

 of the fabric. 



Knowing that the soil retention ability of a fabric is directly related 

 to the hydraulic pressures, flows and forces it encounters, Calhoun (1972) 

 conducted hydraulic filtration and clogging studies to develop a formula 

 that related the EOS to required performance criteria. For geotextile 



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